A unit of speed used to indicate the speed of aircraft, and of spacecraft within the atmosphere. Mach 1 is traveling at the speed of sound; Mach 2, twice the speed of sound, and so on. In dry air at 0�C, the speed of sound is 1,193.3 kilometers per hour (741.5 miles per hour).
Nonmilitary aircraft are not permitted to reach Mach 1 over the United States. The British-French Concorde airliner did reach supersonic speeds on its transoceanic flights, and had a Mach meter on the forward bulkhead of its passenger cabin.
| home | | | units index | | | to contact Sizes  | | | acknowledgements | | | help | | |
Copyright � 2000 Sizes, Inc. All rights reserved.
Last revised: 10 May 2004.